Conventional power amplifiers of this Class comprise several cascaded transistor stages, i.e. an input transistor driven by the signal to be amplified, a control transistor having its base connected to the collector of the input transistor, and an output transistor whose base is tied to the emitter of the control transistor. The emitter of the input transistor, whose conductivity type (e.g. PNP) is opposite that of the other two transistors, is connected to a bus bar of a d-c power supply in parallel with the collectors of the control and output transistors. The peak of the output voltage, occurring upon saturation of the input transistor, falls short of the supply potential by the sum of the saturation voltage drop across the input transistor and the base/emitter voltages of the control and output transistors.
In order to reduce the loss in signal strength represented by this voltage difference, it has already been proposed to separate the emitter of the input transistor and the collector of the control transistor from the associated supply bus bar by a resistor of a magnitude substantially greater than that of a load resistance energized by the output transistor and to feed back the emitter potential of the output transistor through a coupling condenser to the emitter of the input transistor. Such a system, known as a bootstrap circuit, drives the output transistor to saturation at the signal peaks but requires the use of a large capacitor (usually of the electrolytic type) in the feedback path and also causes the dissipation of energy in the isolating resistor. This system is therefore difficult or impossible to realize with a monolithic integrated circuit.